Electromagnetic Torques, Precession and Evolution of Magnetic Inclination of Pulsars

We present analytic calculations of the electromagnetic torques acting on a magnetic neutron star rotating in vacuum, including near-zone torques associated with the inertia of dipole and quadrupole magnetic fields. We incorporate these torques into the rotational dynamics of a rigid-body neutron star, and show that the effects of the inertial torque can be understood as a modification of the moment of inertia tensor of the star. We apply our dynamical equation to the Crab pulsar, investigating the possibility that the counter-alignment of the magnetic inclination angle, as suggested by recent observations, could be explained by pulsar precession. We find that under certain conditions conditions (which require some fine tuning), precession may account for the observed counter-alignment over decade timescales, while the magnetic inclination angle always decreases over the spin-down time of the pulsar.